Electron microscopes are widely used in micro-analysis because of their high depth of field and resolution. Typically, existing electron microscopes use electron-emitter materials that have a high evaporation or sublimation rate in environments that contain oxygen, such as tungsten or lanthanum hexaboride. Consequently, to extend the life of the electron emitter, during operation these existing electron microscopes usually maintain reduced pressures in the high to ultra-high vacuum region (for example, between 10−5 and 10−11 Torr) in a region around the electron emitter. Indeed, as the oxygen pressure in this region in existing electron microscopes is increased from 10−5 to 10−2 Torr, the lifetime of the electron emitter decreases from several hundred hours to less than one hour.
However, the vacuum pumps and associated hardware (such as valves) used to create and maintain such reduced pressures (such as turbo-molecular pumps or diffusion pumps) are expensive, can make existing electron microscopes difficult to use, and can increase the size and weight of the existing electron microscopes. These characteristics can limit the number of potential applications and users of electron microscopes.
Therefore, there is a need for an electron microscope without the problems listed above.